The invention relates to a non-magnetic metal sorting system using a shifting magnetic field to select non-magnetic metals from a mixture including them.
The use of a shifting electromagnetic field is known to separate and select non-magnetic metals from a mixture having its iron component removed by means of magnets for the purpose of resource recovery from solid waste. For this purpose, there have been proposed in the art several apparatuses schematically shown in FIGS. 1 through 5. One example shown in FIG. 1 employs a shifting electromagnetic field generator to produce an electromagnetic force acting in the direction indicated by the arrow a on the mixture including non-magnetic metal particles. The mixture supplied from a chute 1 and transported by means of a belt conveyer 2 so that the non-magnetic metal particles are moved in the direction indicated by the arrow b and the remainder of the mixture is moved in the direction indicated by the arrow c.
The apparatus shown in FIG. 2 includes a shifting electromagnetic field generator 3 to produce an electromagnetic force in the direction indicated by the arrow a so that the non-magnetic metal particles are accelerated in the same direction as the direction of travel of the belt conveyer 2 and discharged in a position removed from the belt conveyer 2 as indicated by the arrow b while the remainder of the mixture is discharged in a position near the belt conveyer 2 as indicated by the arrow c.
In the FIG. 3 apparatus, a shifting electromagnetic field generator 3 is used to produce an electromagnetic force exerted in a direction opposite to the direction of travel of the belt conveyer 2. The non-magnetic metal particles are discharged as shown by the arrow b and the remainder of the mixture is discharged as shown by the arrow c.
Such conventional non-magnetic metal separating apparatus generally provide a satisfactory separation of non-magnetic metal particles from the mixture, but where the non-magnetic metal particles are a different size from the remainder of the mixture, the conventional apparatus do not perform well. Where the size of the non-magnetic metal particles is relatively smaller than that of the remainder, the non-magnetic metal particles will be held between the larger particles of the remainder and cannot be effectively separated therefrom by the electromagnetic force acting on the non-magnetic metal particles. On the contrary, where the size of the non-magnetic metal particles is relatively larger than that of the remainder, the non-magnetic metal particles will trap the smaller particles of the remainder.
In order to obviate the above-mentioned drawbacks the applicant has provided an apparatus capable of selecting non-magnetic metals from a mixture regardless of the relative size of the non-magnetic metal particles. This device is disclosed in Applicant's pending U.S. patent application Ser. No. 843,914 filed on Oct. 20, 1977, and entitled "NON-MAGNETIC METAL SELECTING METHOD AND APPARATUS." This prior art system operates by introducing a mixture including non-magnetic metals through a chute into a rotary drum inclined at an angle with an arch-shaped shifting electromagnetic file generator covering the bottom outer surface of the drum to produce a shifting magnetic field in a direction opposite to the direction of rotation of the drum. As a result, the non-magnetic metals and the remainder of the mixture are fully stirred during the transportation of the mixture through the rotary drum thereby facilitating the selection of the non-magnetic metals from the mixture and providing an accurate selection of non-magnetic metals from the mixture.
This conventional apparatus is shown in FIGS. 4 and 5 wherein FIG. 5 is a sectional view of the conventional metal sorting apparatus taken along the line A--A of FIG. 4. In FIG. 4, the mixture including non-magnetic metal particles transported on a belt conveyer 4 is supplied through a chute 1 into a rotary drum 5 made of an electrically insulative material. The drum 5 is supported through support rods 6 by an iron core 7 through which a rotary shaft 8 extends so that the drum 5 is rotated in the clockwise direction indicated by the arrow e in FIG. 5 as the rotary shaft 8 is rotated by drive means 9. The support rods 6 are preferably made in a cylindrical form and as slender as possible to permit the free movement of the mixture including non-magnetic metal particles. As arch-shaped shifting field generator 10 is disposed just under the lower side of the rotary drum 5 to cover 1/3 to 1/2 of the outer peripheral surface of the drum 5 to produce a shifting electromagnetic field in the counterclockwise direction indicated by the arrow a in FIG. 5 opposite to the direction of rotation of the drum 5. The rotary drum 5 is inclined at an angle determined such that the mixture including non-magnetic metal particles does not pass by its weight through the rotary drum 5 in a short time. The mixture travels therethrough and is brought upwardly in the direction of arrow e along the inner surface of the drum 5 due to the frictional force between the mixture and the drum inner surface or upwardly in the direction of arrow a along the inner surface of the drum 5 due to the electromagnetic force produced by the shifting field generator. It then falls by its weight thereby providing a complete stirring of the mixture within the drum so as to separate the non-magnetic metal particles from the mixture.
That is, the mixture other than the non-magnetic metal particles is lifted along the inner surface of the drum 5 while the frictional force between the mixture and the drum inner surface overcomes the weight thereof and then tumbles down onto the bottom of the rotary drum 5 and again is lifted up along the drum inner surface due to the frictional force. This is repeated so that the mixture other than the non-magnetic particles reaches the downstream end of the rotary drum 5 through the path indicated by the broken arrow d in FIG. 4. On the other hand, the non-magnetic metal particles are subjected to the electromagnetic force produced by the shifting magnetic field generator 10 to move in the direction opposite to the direction of rotation of the cylindrical drum 5 because the electromagnetic force overcomes the frictional force between the non-magnetic metal particles and the drum inner surface.
Since the shifting magnetic field generator 10 is disposed to cover the lower part of the drum 5 as shown in FIG. 5, the part of the non-magnetic metal particles sent beyond the range in which the shifting electromagnetic field exists is returned to the range of the electromagnetic field due to the weight thereof, and the non-magnetic metal particles are again subject to the action of the electromagnetic force. This is repeated until the non-magnetic metal particles reach the downstream end the rotary drum 5. Accordingly, because the shifting magnetic field is directed as indicated by the arrow a and the rotary drum 5 is rotated in the direction as indicated by the arrow e in FIG. 5, the non-magnetic metal particles are separated to the right as indicated by the block particles and the remainder of the mixture is separated to the left as indicated by white particles at the downstream end of the drum 5.
At the downstream end of the rotary drum 5, the non-magnetic metal particles and the remainder of the mixture can separately fall down. The separation plate 11 in contact with the drum inner surface at the boundary between the non-magnetic metal particles and the remainder of the mixture is effective to adequately separate them.
In the conventional device shown in FIGS. 4 and 5, the iron core 7 would be effective in order to increase the exciting-magnetic force of the shifting magnetic field generator 10. However, in the case where a large mass of solid waste are supplied into the rotary drum 5, the iron core 7 and the support rods 6 may prevent these wastes including non-magnetic metal from smoothly passing through the drum 5. Further, sorting efficiency would deteriorate since the non-magnetic metal moved in the direction opposite to the direction of the rotation of the cylindrical drum 5 would be forcibly moved to the rotating direction of the drum 5 by the support rods.
Furthermore, non-magnetic metals moved in the direction opposite to the direction of the rotation of the drum 5 by the shifting magnetic field generator 10 may immediately tumble down on the drum surface due to gravity and frictional forces caused by drum rotation. Upon passing over the generator 10 its electro-magnetic force would be severly decreased so that the non-magnetic metal may move in the direction of rotation of the drum 5, to thereby degrade sorting efficiency. The sorting operation would also be interrupted since relatively large materials would be pinched by the drum 5 and the separation plate 11.